U.S. patent application number 13/226991 was filed with the patent office on 2012-03-08 for head tracking system.
This patent application is currently assigned to Harman Becker Automotive Systems GmbH. Invention is credited to Wolfgang Hess, Thorsten Mayer.
Application Number | 20120057150 13/226991 |
Document ID | / |
Family ID | 43536586 |
Filed Date | 2012-03-08 |
United States Patent
Application |
20120057150 |
Kind Code |
A1 |
Hess; Wolfgang ; et
al. |
March 8, 2012 |
HEAD TRACKING SYSTEM
Abstract
A head tracking system for determining a head position of a user
may include a light source configured to emit light onto a
rectangular position sensitive device supported by a support
structure such as headphones. The light emitted by the light source
may generate a light spot on the position sensitive device. A head
position determining module may determine the head position using
the position of the light spot on the position sensitive device.
The support structure may be configured to support the position
sensitive device such that a head rotation results in rotation of
the position sensitive device and a displacement of the light spot
toward a corner of the rectangular position sensitive device.
Inventors: |
Hess; Wolfgang; (Karlsbad,
DE) ; Mayer; Thorsten; (Remchingen, DE) |
Assignee: |
Harman Becker Automotive Systems
GmbH
Karlsbad
DE
|
Family ID: |
43536586 |
Appl. No.: |
13/226991 |
Filed: |
September 7, 2011 |
Current U.S.
Class: |
356/138 ;
356/615 |
Current CPC
Class: |
G06F 3/012 20130101;
H04R 5/04 20130101; G02B 27/0093 20130101; G01S 5/163 20130101;
G01S 3/784 20130101; G01S 1/70 20130101; H04S 7/304 20130101 |
Class at
Publication: |
356/138 ;
356/615 |
International
Class: |
G01B 11/26 20060101
G01B011/26; G01B 11/14 20060101 G01B011/14 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 8, 2010 |
EP |
10 175 803.5 |
Claims
1. A head tracking system for determining a head position of a
user, the system comprising: a light source positioned at a fixed
point; a planar rectangular position sensitive device supported by
a support structure, the light source configured to generate a
light spot on the position sensitive device; and a head position
determining module configured to determine the head position based
on a position of the light spot on the position sensitive device,
where a surface normal of the position sensitive device in a head
rest position points at the light source, and a diagonal between a
pair of opposing corners of the position sensitive device in the
head rest position is oriented substantially horizontally such that
rotation of the position sensitive device in a substantially
horizontal plane away from the head rest position results in a
displacement of the light spot towards one of the pair of opposing
corners of the position sensitive device.
2. The head tracking system according to claim 1, where the
position sensitive device is a square position sensitive device,
and the support structure supports the square position sensitive
device such that rotation of the position sensitive device in the
horizontal plane away from the head rest position results in the
displacement of the light spot on the diagonal of the square
position sensitive device.
3. The head tracking system according to claim 1, where the support
structure supports the position sensitive device on an apex of the
position sensitive device.
4. The head tracking system according to claim 1, where the head
position determining module is configured to determine a yaw angle
corresponding to a rotational position of the position sensitive
device relative to the light source along the horizontal plane away
from the head rest position based on the position of the light spot
relative to the diagonal.
5. The head tracking system according to claim 1, where the pair of
opposing corners is a first pair of opposing corners and the
diagonal is a first diagonal, a second diagonal between a second
pair of opposing corners of the position sensitive device in the
head rest position is oriented substantially vertically such that
rotation of the position sensitive device in a substantially
vertical plane away from the head rest position results in a
displacement of the light spot towards one of the second pair of
opposing corners of the position sensitive device, the head
position determining module is configured to determine a yaw angle
corresponding to a first rotational position of the position
sensitive device relative to the light source along the horizontal
plane away from the head rest position based on the position of the
light spot relative to the first diagonal, and the head position
determining module is configured to determine a pitch angle
corresponding to a second rotational position of the position
sensitive device relative to the light source along the vertical
plane away from the head rest position based on the position of the
light spot relative to the second diagonal.
6. The head tracking system according to claim 1, where the head
position determining module is configured to calculate a yaw angle
corresponding to a rotational position of the position sensitive
device relative to the head rest position based on the position of
the light spot on the position sensitive device.
7. The head tracking system according to claim 1, where the head
position determining module is configured to determine a position
of the light spot relative to the diagonal of the position
sensitive device and retrieve a yaw angle corresponding to the
position of the light spot relative to the diagonal.
8. The head tracking system according to claim 1, where the
determined head position is independent of an intensity of the
light spot on the position sensitive device.
9. A system for generating a virtual surround sound signal, the
system comprising: a light source positioned at a fixed point; a
planar rectangular position sensitive device supported by a support
structure, the light source configured to generate a light spot on
the position sensitive device; a head position determining module
configured to determine a head position based on a position of the
light spot on the position sensitive device; a filter database
comprising a plurality of filter elements, each filter element
corresponding to a defined head position; and an audio signal
processing module configured to receive an audio input signal,
select at least one of the plurality of filter elements
corresponding to the determined head position, filter the received
audio input signal with the selected at least one filter element,
and generate the virtual surround sound signal, where a surface
normal of the position sensitive device in a head rest position
points at the light source, and a diagonal between a pair of
opposing corners of the position sensitive device in the head rest
position is oriented substantially horizontally such that rotation
of the position sensitive device in a substantially horizontal
plane away from the head rest position results in a displacement of
the light spot towards one of the pair of opposing corners of the
position sensitive device.
10. The system according to claim 9, where the head position
determining module is configured to calculate a yaw angle
corresponding to a rotational position of the position sensitive
device relative to the head rest position based on the position of
the light spot on the position sensitive device.
11. The system according to claim 9, where the head position
determining module is configured to determine a position of the
light spot relative to the diagonal of the position sensitive
device and retrieve a yaw angle corresponding to the position of
the light spot.
12. The system according to claim 9, where each of the plurality of
filter elements corresponds to an impulse response determined for
the corresponding defined head position.
13. The system according to claim 9, where the head position is a
first head position and the position of the light spot on the
position sensitive device is a first position of the light spot on
the position sensitive device, the head position determining module
further configured to determine a second head position based on a
second position of the light spot on the position sensitive
device.
14. The system according to claim 13, where the selected at least
one filter element is a first at least one filter element
corresponding to the first head position, the audio signal
processing module further configured to select a second at least
one filter element corresponding to the second head position,
filter the received audio input signal with the second at least one
filter element, and adjust the virtual surround sound signal.
15. A method for determining a head position of a user, the method
comprising the steps of: emitting light with a light source toward
a rectangular planar position sensitive device supported by a
support structure, a diagonal between a pair of opposing corners of
the position sensitive device being oriented substantially
horizontally; generating a light spot on the position sensitive
device with the emitted light; sensing a rotation of the position
sensitive device in a substantially horizontal plane based on a
displacement of the light spot towards one of the pair of opposing
corners of the position sensitive device; and determining the head
position based on a position of the light spot on the position
sensitive device.
16. The method according to claim 15, where the position sensitive
device is a square position sensitive device and sensing the
rotation of the position sensitive device in the horizontal plane
comprises sensing the displacement of the light spot on the
diagonal of the square position sensitive device.
17. The method according to claim 15, where determining the head
position comprises calculating a yaw angle corresponding to a
rotational position of the position sensitive device based on the
position of the light spot on the position sensitive device.
18. The method according to claim 15, where determining the head
position comprises determining a position of the light spot
relative to the diagonal of the position sensitive device and
retrieving a yaw angle corresponding to the position of the light
spot relative to the diagonal.
19. The method according to claim 15, where the determined head
position is independent of an intensity of the light spot on the
position sensitive device.
20. A method for generating a virtual surround sound signal, the
method comprising the steps of: emitting light with a light source
toward a rectangular planar position sensitive device supported by
a support structure, a diagonal between a pair of opposing corners
of the position sensitive device being oriented substantially
horizontally; generating a light spot on the position sensitive
device with the emitted light; sensing a rotation of the position
sensitive device in a substantially horizontal plane based on a
displacement of the light spot towards one of the pair of opposing
corners of the position sensitive device; determining a head
position based on a position of the light spot on the position
sensitive device; determining a filter element corresponding to the
determined head position; receiving an audio input signal; and
filtering the audio input signal with the determined filter element
to generate the virtual surround sound signal.
21. The method according to claim 20, where determining the head
position comprises calculating a yaw angle corresponding to a
rotational position of the position sensitive device based on the
position of the light spot on the position sensitive device.
22. The method according to claim 20, where determining the head
position comprises determining a position of the light spot
relative to the diagonal of the position sensitive device and
retrieving a yaw angle corresponding to the position of the light
spot.
23. The method according to claim 20, where determining a filter
element comprises determining an impulse response corresponding to
the determined head position.
24. The method according to claim 20, where the head position is a
first head position and the position of the light spot on the
position sensitive device is a first position of the light spot on
the position sensitive device, the method further comprising
determining a second head position based on a second position of
the light spot on the position sensitive device.
25. The method according to claim 24, where the determined filter
element is a first filter element corresponding to the first head
position, the method further comprising determining a second filter
element corresponding to the second head position, filtering the
received audio input signal with the second filter element, and
adjusting the virtual surround sound signal.
Description
PRIORITY CLAIM
[0001] This application claims the benefit of priority from
European Patent Application No. 10 175 803.5, filed Sep. 8, 2010,
which is incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field
[0003] The present application relates to a head tracking system
for determining a head position of a user and to a sound system for
generating a virtual surround sound for the user using the head
tracking system.
[0004] 2. Related Art
[0005] Head tracking systems detect different types of movements of
the head. By way of example, a head tracking system may detect a
turning of the head around the longitudinal axis of the head, i.e.
in a horizontal plane of the head.
SUMMARY
[0006] A head tracking system may determine the head position of a
user. The system may include a light source emitting a light onto a
planar rectangular position sensitive device provided in a support
structure, the light emitted by the light source generating a light
spot on the position sensitive device. A head position determining
module may determine the head position based on the position of the
light spot on the position sensitive device.
[0007] Other systems, methods, features and advantages will be, or
will become, apparent to one with skill in the art upon examination
of the following figures and detailed description. It is intended
that all such additional systems, methods, features and advantages
be included within this description, be within the scope of the
invention, and be protected by the following claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The system may be better understood with reference to the
following drawings and description. The components in the figures
are not necessarily to scale, emphasis instead being placed upon
illustrating the principles of the invention. Moreover, in the
figures, like referenced numerals designate corresponding parts
throughout the different views.
[0009] FIG. 1 shows a schematic view of a head tracking system
generating a virtual surround sound for a user using the
headphones.
[0010] FIG. 2 shows an example of a position sensitive device
arranged in one exemplary arrangement.
[0011] FIG. 3 shows an example of a position sensitive device
arranged in another exemplary arrangement.
[0012] FIG. 4 shows a schematic view of an example of an audio
system with a head tracking system for generating a virtual
surround sound.
[0013] FIG. 5 shows a schematic view explaining an example of the
generation of a virtual surround sound using headphones.
[0014] FIG. 6 shows exemplary audio signals of a left and right
channel recorded for the generation of filter elements used to
generate a virtual surround sound.
[0015] FIG. 7 is a diagram explaining the functioning of an
exemplary position sensitive device.
[0016] FIG. 8 shows an example of current outputs of a position
sensitive device.
[0017] FIG. 9 shows a flow chart describing exemplary steps for
generating a virtual surround sound for a user.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] A head tracking system may include a position sensitive
device and a light source, such as a light emitting diode (LED)
used for detecting the relative position of a human head. The
system may be sufficient to detect relatively small head rotations
of approximately +/-20.degree.. The head position may be determined
by the use of one single position sensitive device in a range
sufficient to cover usual head movements of a user, e.g. in a
vehicle.
[0019] In one example, the head tracking system may determine the
head position of a user. The system may include a light source
emitting a light onto a planar rectangular position sensitive
device provided in a support structure. The light emitted by the
light source may generate a light spot on the position sensitive
device. A head position determining module may determine the head
position based on the position of the light spot on the position
sensitive device. The support structure may be designed to support
the position sensitive device such that, in a head rest position
where a surface normal of the planar rectangular position sensitive
device points at the light source, a diagonal between a pair of
opposing corners of the position sensitive device is oriented
horizontally such that a head rotation in the horizontal plane
results in a displacement of the light spot towards one corner of
the rectangular position sensitive device. This orientation of the
position sensitive device by the support structure may increase the
range of head rotations or nodding movements of a head that can be
detected.
[0020] In another example, the position sensitive device may be
oriented such that a head rotation results in a displacement of a
light spot to an edge of the position sensitive device. By turning
the position sensitive device with an angle of 45.degree. relative
to such an orientation as described above, the detection range may
be increased. The position of the light spot on the position
sensitive device may provide a measure for the head rotation. As
the distance between two opposite corners of a rectangular position
sensitive device is larger than the distance between two edges of
the rectangular position sensitive device, a larger range of head
rotations can be detected. With the improved position of the
position sensitive device, head rotations of around +/-45.degree.
relative to the straight forward looking position, i.e., the head
rest position or reference position, can be detected.
[0021] The position sensitive device may be a square position
sensitive device, the support structure supporting the square
position sensitive device in such a way that a head rotation in the
horizontal or vertical plane results in a displacement of a light
spot on a diagonal of the square position sensitive device. For
example, the support structure can support the position sensitive
device on an apex of the position sensitive device. A diagonal of
the position sensitive device may be oriented substantially
horizontally. The light source may be arranged relative to the
position sensitive device in such a way that when the user looks
straight ahead, the light spot is located proximate the center of
the square position sensitive device. This may define the head rest
position where a surface normal of the planar rectangular position
sensitive device points at the light source. For example, in the
head rest position, the surface normal of the position sensitive
device may be a vector perpendicular to the surface of the position
sensitive device and having a direction pointing toward the light
source. When the user rotates the head in one direction in the
horizontal plane, the light spot is moved along the diagonal in one
direction, whereas, when the user rotates the head in the other
direction, the light spot moves on the diagonal in the other
direction.
[0022] The head position determining module can be configured to
determine a yaw angle of the head corresponding to a turning of the
head in the horizontal plane, where the light source is positioned
relative to the position sensitive device in such a way that the
turning of the head results in a displacement of the light spot on
one diagonal (e.g., a horizontal diagonal) of the position
sensitive device. The position sensitive device then may determine
the yaw angle from the position of the light spot relative to said
one diagonal. Furthermore, in addition to the yaw angle, the
position determining module can be further configured to determine
the pitch angle of the head corresponding to a nodding movement of
the head, where the light source is positioned relative to the
position sensitive device in such a way that the nodding of the
head results in a displacement of the light spot on the other
diagonal (e.g., a vertical diagonal) of the position sensitive
device, the position sensitive device determining the pitch angle
from a position of the light source relative to said other
diagonal. In this example the head positioning determining module
may determine an angle describing the rotation of the head in the
horizontal plane relative to the straight looking or relatively
horizontal position of the head and additionally may determine an
angle describing whether the user is looking up or down. In other
words, the azimuth and the elevation angle of the head rotational
angles may be determined.
[0023] Especially when the head tracking system is used in
connection with a head-phone based sound system generating a
virtual surround sound for a user, the determination of the azimuth
angle, the yaw, may be the most important angle, as the change of
the azimuth angle changes the interaural time differences and the
interaural level differences which are the most prominent
localization cues used by the human brain for localizing a sound
source. Thus, the nodding movement, i.e. the elevation angle, is
not necessarily determined, as it can be sufficient to only
determine the azimuth angle.
[0024] A sound system may generate a virtual surround sound for a
user using standard headphones. Alternatively, the system may be
configured for use with any other type of loudspeaker or other
sound generation device. The system may include a head tracking
system as described above and a filter database containing a
plurality of filter elements, each filter element corresponding to
a defined head position. Furthermore, an audio signal processing
module may be provided for receiving an audio input signal from an
audio source such as a CD, a radio, a vehicle head unit, a wireless
communication device, or any other source of a single or
multi-channel audio content. The audio signal processing module
also may generate the virtual surround sound for the headphones.
The audio signal processing module receiving the determined head
position may be configured to select the filter element of the
determined head position and/or to filter the audio input signal
with the selected filter element in order to generate the virtual
surround sound for the user. The sound system can be used with any
commercial available headphone. The headphone does not have to be a
dedicated headphone, i.e. it needs only one loudspeaker per
headphone side, but can also use more than one.
[0025] The system also may include a method for determining a head
position of a user, which may include the steps of emitting by a
light source light onto a rectangular position sensitive device
provided in a support structure, the light emitted by the light
source generating a light spot on the position sensitive device.
The position sensitive device may be arranged on a support
structure such as headphones in such a way that a head rotation
results in a displacement of the light spot to a corner of the
rectangular position sensitive device. The position of the light
spot on the position sensitive device may be used to determine the
head position.
[0026] The position sensitive device can be a square position
sensitive device that is supported by the support structure in such
a way that the head rotation results in a displacement of a light
spot on the diagonal of the square position sensitive device.
[0027] In FIG. 1 a head tracking system is schematically shown. The
head tracking system includes one or more light sources 10 emitting
light to one or more position sensitive devices 100 installed on
headphones 20. The light source 10 can be a light emitting diode
(LED) emitting light in a predetermined frequency range, e.g.
infrared light in a pulsed way. In other examples, other sources of
light such as sunlight, incandescent lamps, fluorescent lamps, high
intensity discharge lamps, gas discharge lamps, lasers, or any
other light sources are possible. The infrared frequency range may
be used in order not to disturb a user wearing the headphones 20.
As will be explained with reference to FIGS. 2-4 in further detail
below, the light emitted by the LED 10 may generate a light spot on
the position sensitive device 100. The position of the light spot
on the position sensitive device may be used to determine the head
position of the user wearing the headphones. The LED 10 may be
arranged at a fixed location and may transmit the light in the
direction of the user wearing the headphones. The system shown in
FIG. 1 may be part of a rear seat vehicle entertainment system in
which a user sitting on the back seat of a vehicle hears music or
watches a film, the audio signals of which are emitted as audible
sound using the headphones 20. With the present disclosure it is
possible to generate a virtual surround sound for the user wearing
the headphones as will be explained with reference to FIG. 5.
[0028] Determination of the head position may enable the generation
of a virtual surround sound. In a virtual surround sound using
headphones, a listening impression may be generated as if the user
used a 5.1 or 7.1 loudspeaker sound system as shown in FIG. 5,
showing a system of 5 loudspeakers 50. The virtual surround sound
field may give the impression as if the sound source is stable
localized in the virtual room. This phenomena, known as acoustical
room-constancy, allows the user using headphones to determine the
stable direction from where the sound is coming. Also the user
experiences an interactive listening process with the system when
turning the head, corresponding to the real-world situation, since
it is possible to localize the sound source stable outside of the
head with correct front/back position.
[0029] Perfect externalized, realistic localization may become
possible listening through standard headphones 20. This may be
caused by tracking the position of the head and by determining a
filter for the determined head position which are used for a
low-latency blockwise convolution of the sound signal with the
filter in real time.
[0030] These filter elements can be generated in the following way:
using a dummy head with microphones in each ear, the binaural room
impulse responses may be measured. To this end the dummy head
placed on a manikin or a stand is positioned in the location, e.g.
in the vehicle where the system should be used. Different positions
of the dummy head, e.g. different rotations, are used and, for each
head position, the loudspeakers 50 as shown in FIG. 5, output a
sound that is detected by the microphones in the dummy head. This
may be repeated for different head rotations, e.g. in steps of
1.degree., until the azimuth angle of +/-45.degree. is measured. In
FIG. 6 the impulse response as measured in the two ears of the
dummy head for a defined head position are shown, signal 61 showing
the impulse response for the left channel/left ear, signal 62
showing the impulse response for the right channel/right ear. The
signals shown in FIG. 6 describe the signals output from one of the
loudspeakers of FIG. 5 to the left and the right ear of the dummy
head. The audio signals are detected for each of the loudspeakers
50 and for the different head positions generating a plurality of
impulse responses. Based on the impulse responses, at least one
filter element is determined for each head position. When a stereo
sound signal is then filtered using a filter for a determined head
position by determining a real-time convolution of the audio signal
with the filter element, the virtual surround sound can be obtained
in which the user using head phones has the impression as if the
audio signals came from a sound system as shown in FIG. 5.
[0031] The head tracking system that is used to generate the
virtual surround sound using the headphones will now be explained
in more detail with reference to FIGS. 2-4 and 7-8.
[0032] In FIG. 2 a position sensitive device 100' in one exemplary
orientation is shown. Light emitted by a light source, such as the
LED 10, may be focused on the position sensitive device 100' using
a lens (not shown). The position sensitive device which is
positioned in the focal plane of the lens receives the light
emitted by the light source and a light spot is generated on the
position sensitive device. The light source 10 may be positioned in
such a way that when the user looks straight ahead, the light spot
is located somewhere on the x-y-axis shown in FIG. 2. This may
correspond to a head rest position where a surface normal of the
planar rectangular position sensitive device points at the light
source. An implementation of the position sensitive device 100'
will be explained in more detail with reference to FIG. 7.
[0033] In the upper part of FIG. 7 a cross sectional view of the
position sensitive device is shown. The device 100' may include an
extending pin structure, P indicating a P-doped semiconductor
layer, I designating a nominally undoped or low-doped (insulating)
semiconductor layer and N designating an N-doped semi-conductor
layer. A back contact k0 may be coupled with the N-doped layer of
the structure approximately in a middle of the N-doped layer.
Opposing side contacts k1 and k2 may contact the P-doped layer. In
order to provide a two-dimensional sensing, additional contacts
(not shown) may be provided in a direction perpendicular to the
contacts shown.
[0034] Such a device may use the so-called lateral photo effect for
position sensing. A total current is supplied via contact k0. An
arrow labeled .PHI. indicates a position where light falls on the
sensor. At the area where light falls on the sensor, the device
becomes conducting in a transverse direction (e.g., an
up-down-direction in FIG. 7). In the p-axis in the middle of FIG.
7, this location is designated P1.
[0035] Assuming that the resistance of the N-doped layer is low,
the resistance from k0 to k1 and k2 (Rq1 and Rq2, respectively, as
shown in the lower part of FIG. 7) are determined by the position
P1 where light falls on the sensor. Currents I1, I2 detected at k1,
k2, respectively, are indicative of the position P1. In particular,
in the dimension shown, the position P1 relative to the middle of
the sensor is proportional to (I1-I2)/(I1+I2).
[0036] Similar considerations hold true for the two-dimensional
sensor. With the above described position sensitive device, the
above given ratio of currents may be independent of the light
intensity received by the sensor, such that the distance from the
light source to the position sensitive device does not influence
the result.
[0037] Referring back to FIG. 2, this means that a light spot in
the active area of the sensor having a length L may describe the
head rotation alone (in a one-dimensional case) or the head
rotation and the "nodding position" of the head in case of a two
dimensional sensor. However, in the example of FIG. 2 the position
of the light spot may be limited to +/-L/2 in the x and y
direction. This limitation may result from the fact that, if the
distance between the position P1 of the light spot and the middle
of the sensor is greater than L/2 in either direction, the light
spot may be positioned off of the sensor (i.e., the light spot may
not contact the sensor, and the sensor may be unable to detect the
light spot).
[0038] In FIG. 3 another exemplary orientation of the position
sensitive device is shown. Compared to the example shown in FIG. 2,
the device may be rotated by 45.degree.. This rotation may enable
the positioned sensitive device to be supported on an apex or
corner of the position sensitive device as shown in FIG. 3. The
position sensitive device may be supported by a support structure
200 in such a way that a rotation of a head in the horizontal plane
(i.e., rotation of the position sensitive device about a vertical
axis of the sensor in the horizontal plane) may result in a
displacement of the light spot along one of the axes X', Y',
whereas the nodding movement of the head (i.e., rotation of the
position sensitive device about a horizontal axis of the sensor in
a vertical plane) may result in a displacement of the light spot on
the position sensitive device 100 along the other of the axes X' or
Y'. Rotation of the head may cause the position sensitive device to
rotate about the vertical axis of the position sensitive device in
a substantially horizontal plane. Nodding of the head may cause the
position sensitive device to rotate about the horizontal axis of
the position sensitive device in a substantially vertical plane.
Combined rotation and nodding of the head may cause the position
sensitive device to rotate about the vertical axis and the
horizontal axis of the position sensitive device. As can be
deduced, when the axis X' is compared with axis x, a larger range
of detection may be obtained so that greater head movements can be
detected. For example, because a diagonal of a rectangular sensor
100 may have a greater length than the sides of the sensor, the
axes X', Y' may have greater lengths than the corresponding axes x,
y of the sensor 100' having substantially the same size and shape
(but a different orientation) than the sensor 100.
[0039] As described in connection with FIGS. 7-8 the output of the
position sensitive device may be the currents I.sub.1, I.sub.2 for
the one-dimensional case and I.sub.1, I.sub.2, I.sub.3 and I.sub.4
for the two-dimensional case. FIG. 8 shows one example of a
two-dimensional position sensitive device. The currents I.sub.1,
I.sub.2, I.sub.3 and I.sub.4 may be measured at points
corresponding generally to the corners of the position sensitive
device. The position of the light spot using a coordinate system as
shown in FIG. 2 can be calculated as follows
X = ( I 2 + I 3 ) - ( I 1 + I 4 ) I 1 + I 2 + I 3 + I 4 L 2 ( 1 ) Y
= ( I 2 + I 4 ) - ( I 1 + I 3 ) I 1 + I 2 + I 3 + I 4 L 2 . ( 2 )
##EQU00001##
[0040] Using the system as shown in FIG. 3 with X' and Y', the
transformation from X to X' and Y to Y' is as follows:
X ' = ( Y + X ) 2 2 . ( 3 ) Y ' = ( Y - X ) 2 2 . ( 4 )
##EQU00002##
[0041] In connection with FIG. 4 it is explained in more detail how
the head position is calculated. The head tracking system may be
provided with a plurality of modules, units, and/or components. The
head tracking system may include a computing device or computer,
including for example software, hardware, or a combination of
hardware and software capable of performing the described
functionality. The head tracking system may be one or more separate
systems or devices, may be one or more systems or devices included
in another system, or may be combined with other systems or devices
within the other system. The computing devices and modules of the
head tracking system may be fully contained in the headphones.
Alternatively, at least a part of the computing device(s) and/or
modules of the head tracking system may be located external to the
headphones, such as at the light source 10, in the audio system, or
at some other location. In other examples, fewer or additional
blocks may be used to illustrate the functionality of the head
tracking system. The modules, units and/or components of the head
tracking system may include a light source 10, a lens 110, a
position sensitive device 100, headphones 20, a voltage converter
120, a high-pass filter 130, an amplifier 140, a low-pass filter
150, an analogue-to-digital converter 160, a head position
determining module 170, an audio signal processor 180, and a filter
database 190.
[0042] The functionality included in the head tracking system may
be modules, components and/or units. The term "module" or
"component" or "unit" may be defined to include one or more
executable parts of a system. As described herein, the modules
and/or units are defined to include software, hardware, or some
combination thereof executable by a processor. The processor may be
implemented as a single or as multiple microprocessors, as a
digital signal processor (DSP), an application-specific integrated
circuit (ASIC) or the like. Software included in the modules and/or
units may include instructions stored in memory or a computer
readable medium that are executable by the processor, or any other
processor. Memory may include all types of memory, such as random
access memory, flash memory, a hard drive, a CD-ROM device, a DVD
device, a ROM memory device, or any other non-transitory data
storage device. In addition, rewritable non-volatile memory, such
as flash memory, may be provided to store processing information in
a flexible way and to maintain the stored information even in the
case of a power outage. Hardware included in the modules and/or
units may include various devices, components, circuits, gates,
circuit boards, and the like that are executable, directed, and/or
controlled for performance by the processor.
[0043] The light source 10 shown in FIG. 1, and not shown in FIG.
4, may emit light in an infrared spectrum. Furthermore, a
modulation circuit for modulating the light emitted by the LED
according to a predetermined pattern may be provided modulating the
emitted light. With such a modulation a light emitted from the LED
may be discerned from light emitted from other sources. The light
may pass through a lens 110 to focus the light on the position
sensitive device 100. In front of the lens 110 an optical filter
may be provided for filtering the received light. The filter may be
a filter which is transparent to infrared light, but opaque for
light of other wavelengths, such as visible light.
[0044] The position sensitive device 100 may be placed in the focal
plane of lens 110 where the light is focused in a light spot. The
device 100 may be installed on the headphones and, depending on the
position of the head, the light of the fixedly installed light
source may be focused on the surface of the position sensitive
device to form a light spot.
[0045] As was explained above in connection with FIG. 8, four
currents I1 to I4 may be generated. These four currents may be fed
to a current voltage converter 120 which converts the current into
voltages. This, for example, may be achieved by measuring the
voltage drop of a resistor having a known resistance through which
the respective current flows. The thus generated voltages may then
be filtered using at least one high-pass filter 130 in order to
filter out DC components and other low frequency components. After
the high-pass filter 130 the high-passed filtered voltages may be
amplified in amplifier 140 before being low-pass filtered in at
least one low-pass filter 150. The low-pass filter together with
the high-pass filter may build a band-pass filter transmitting only
the signals originating from the modulated pulsed infrared light
source. In other examples, other forms of band-pass filter may be
used.
[0046] The signal may then be passed through an analogue-to-digital
converter 160, where the signal is generated in the digital domain.
From the converter 160 the signal may be fed to a head position
determining module where the azimuth angle and the elevation angle
of the head are determined. The head position determining module
may include a conversion unit where the currents (or the
corresponding voltages) are converted into X', Y' location
describing the position of the light spot in the X', Y' system.
This position may then be converted into the azimuth angle (yaw)
and elevation angle in case of a nodding movement (pitch). The head
position determining module may be a processor or other module or
unit configured to determine the azimuth and/or elevation angles
based on the position of the light spot on the position sensitive
device.
[0047] For a generation of the virtual surround sound it may be
sufficient to only determine the yaw, as this head rotation mainly
influences the signal path from the virtual sound source to the
left and right ear. The yaw angle may be the most important angle
as a change of the yaw angle may have the largest influence on the
interaural time difference (ITD) and interaural level difference
(ILD) which are used for the aural localization perception by the
user. Thus, the head position determining module may output one or
two angles, either the yaw angle alone or the yaw and pitch angle.
The conversion of the position X', Y' into angles may be obtained
by using the arctangent. For example, the lateral deviation of the
light spot on the opposition sensitive device may be determined as
described above. The distance between the lens 110 and the device
100 may be known. The azimuth angle (yaw) may be determined as the
arctangent of the lateral deviation of the light spot along one of
the X' and Y' axes divided by the distance between the lens 110 and
the device 100. Similarly, the elevation angle (pitch) may be
determined as the arctangent of the lateral deviation of the light
spot along the other of the X' and Y' axes divided by the distance
between the lens 110 and the device 100. In one example, a table
also may be provided in which the correspondence between different
positions X', Y' and different corresponding angles are stored. The
head position determining module may be configured to correlate the
position of the light spot on the position sensitive device with
the corresponding angles stored in the table. In other examples,
correspondence between different positions X', Y' and different
corresponding angles may be calculated by the processor and the
light spot position correlated. The angles (yaw, pitch) or the
angle (yaw) can be determined, e.g., by the head position
determining module, and transmitted to the processor illustrated as
an audio signal processor 180.
[0048] The yaw and/or pitch angles may be determined based on the
position of the light spot on the position sensitive device. Such a
determination may be made without the use of additional sensors
such as, for example, a gyroscope or tilt sensor. The determination
also may be relatively fast as compared to using multiple or
additional sensors. For example, the calculation of the yaw and/or
pitch angles based on the position of the light spot may be
relatively simple and thus may be completed quickly with little
source code. In some instances, it may be desirable to synchronize
the generated audio signal with a corresponding video signal, such
as when viewing a film using a rear seat vehicle entertainment
system. In these or other situations, the speed of the calculation
may be an important consideration in generating the real time audio
signal.
[0049] The audio signal processor may receive an input, e.g. a
stereo audio input signal. With the determined angle or the
determined angles, the audio signal processor may access a filter
database 190 where the corresponding filters are stored for the
different angles. As discussed in connection with FIGS. 5 and 6 the
filter database may be determined in advance using the dummy head.
For each head position, a filter pair for the left and right audio
signals may be retrieved and the audio input signal may be filtered
using the filter elements for that determined head position.
Alternatively, or in addition, the filters may be dynamically
generated or coefficients of the filters may be adjusted by the
processor using the audio signal processor based on the determined
head position. The audio output signal may be generated by a
convolution of the audio input signal with the filters from the
filter database 190 and then fed to the headphones.
[0050] In FIG. 9 the different steps carried out for determining
the virtual surround sound for the user wearing headphones are
summarized. The method starts in step 80. In step 81 the position
sensitive device, PSD, may be positioned on the headphones as shown
in FIG. 1 and shown in further detail in FIG. 3. The light emitted
by the light source may generate a light spot on the position
sensitive device. In step 82, the position of the light spot may be
determined using the currents I1 to I4 as explained in connection
with FIG. 7. When the position of the light spot in the x', y'
coordinate system is known, the head rotation can be calculated in
step 83. Here, either the azimuth angle or the azimuth angle and
the elevation angle of the user's head may be determined. With the
known head position in step 84 the corresponding filter elements
from the filter database 190 may be determined and/or retrieved,
and in step 85 the audio input signal may be filtered in the audio
signal processor 180 to generate the virtual surround sound for the
user. The method ends in step 86.
[0051] At least a portion of the method may be repeated to adjust
the virtual surround sound signal. For example, the system may
return to step 82 to determine a second position of the light spot
on the position sensitive device. A second head rotation (e.g., a
second azimuth angle and/or a second pitch angle) may be determined
based on the second position of the light spot in step 83. A second
set of corresponding filter elements may be determined and/or
retrieved from the filter database based on the determined second
head rotation in step 84. In step 85, the audio signal may be
filtered using the second set of filter elements, and a second
virtual surround sound signal may be generated (e.g., the virtual
surround sound signal may be adjusted according to the second head
rotation).
[0052] The head tracking system may enable determination of a head
position in a range of approximately +/-45.degree. using a single
position sensitive device. Accordingly, a gyroscope, a compass
and/or an accelerometer may be unnecessary for determining the head
position. Thus, the number of sensors can be greatly reduced by
using only one position sensitive device, such as device 100, that
is oriented as shown in FIGS. 3 and 4 for an improved detection
range.
[0053] While various examples of the invention have been described,
it will be apparent to those of ordinary skill in the art that many
more examples and implementations are possible within the scope of
the invention. Accordingly, the invention is not to be restricted
except in light of the attached claims and their equivalents.
* * * * *